RCD keeps tripping

[brightspark]

i did one yesterday a trapped neutral behind a socket to earth had to take 4 sockets off to find it and test with meter .bout an hours work just take extra care with face of the db off live cables exposed and socket

 

[AVI_8]

The friction of pulling another wire through a tight space can rub through and melt insulation on existing wires. If you've worked near wiring recently then that's likely to be where the fault is.

The broadband cable I pulled through from an outside vent wasn‘t too near the electric cables, but the solum entrance is right under the consumer unit, I’ll check that first then try what @brightspark suggested.

 

[AVI_8]

Got round to fixing this fault today, took the cover off the CU, no problems with the wires there so got the overalls on and went under the floor, I’m fortunate that there’s a 3ft crawl space, traced all of the wires on the main and no sign of damage from rodents anywhere.
Disconnected one live and neutral from the CU as @brightspark suggested until I’d found the fault, with both wires connected to the breaker all of the sockets could be powered, so the fault was in one of the wires between 2 sockets in that room, fed a new wire through and connected up and now all is well, just need to re-plaster as the wires were encapsulated in the plaster so it made a bit of a mess.
The wire I replaced has no obvious signs of damage and with the lives and neutrals connected with wago connections the breaker wasn’t tripping, only when the earths were connected did the RCD trip, so probably as @dobbslc suggested a live to earth fault. In case you’re wondering the cable in the picture is the new cable, I just wanted to test it above ground before fitting it.
Thanks to all who helped, much appreciated.

 

[brightspark]

nice one